Continuous Process for Producing Titanium Tetrachloride Using On-Line Monitoring of Vanadium Oxytrichloride (VolcL3) With Anti-Fouling Management

Abstract

An improved continuous process for producing titanium tetrachloride having a vanadium content of less than 5 ppm using on-line monitoring of vanadium oxytrichloride in crude titanium tetrachloride with effective anti-fouling management of precipitated niobium oxytrichloride.

1 . In a continuous process for recovering titanium tetrachloride from a crude titanium tetrachloride process stream comprising a mixture of metal chlorides comprising titanium tetrachloride, ferrous chloride, aluminum trichloride, vanadium oxytrichloride, and niobium oxytrichloride of the type wherein:
 (a) a titania-containing ore is contacted with chlorine gas at elevated temperature in one or more reaction zones in the presence of petroleum coke to produce a vapor phase off-gas stream;   (b) said vapor phase off-gas stream is condensed to produce a crude liquid phase; and   (c) gaseous chlorine is injected into the vapor phase off-gas stream in response to the concentration of ferrous chloride in said off-gas stream;   the improvement comprising:
 (i) establishing a recycle loop for recycling a portion of said crude titanium tetrachloride process stream; 
 (ii) passing a portion of said crude titanium tetrachloride through said recycle loop; 
 (iii) placing a probe in said recycle loop capable of continuously sensing the concentration of oxychlorides in said crude titanium tetrachloride; 
 (iv) monitoring the concentration of vanadium oxytrichloride in said crude titanium tetrachloride and introducing an amount of vanadium passivating agent into said crude titanium tetrachloride process stream in response to said monitored concentration of vanadium oxytrichloride; 
 (v) simultaneously monitoring the concentration of niobium oxytrichloride that precipitates on the probe in relation to a set point; 
 (vi) interrupting up to 100% of the flow of said crude titanium tetrachloride from said recycle loop when the concentration of niobium oxytrichloride on the probes reaches the set point; 
 (vii) directing a flow of inert gas or a mixed flow of inert gas and titanium tetrachloride at elevated pressure in the range of from 20 psi up to 140 psi onto the probe with sufficient kinetic energy derived from the elevated pressure and flow rate to sweep precipitated niobium ocytrichloride from the probe; 
 (viii) isolating the flow of inert gas and renewing the flow of crude titanium tetrachloride through the recycle loop when the concentration of niobium oxytrichloride on the probe has dropped below the set point. 
   
   
   
       2 . The process of  claim 1  wherein the inert gas is nitrogen or dry air. 
   
   
       3 . The process of  claim 2  wherein the probe is an optical IR probe comprising a zinc selenide window, and the flow of inert gas is directed generally perpendicular to the zinc selenide window. 
   
   
       4 . The process of  claim 4  wherein simultaneously monitoring the concentration of vanadium oxytrichloride and niobium oxytrichloride is accomplished with a method selected from Transmission Filter Infrared Spectroscopy, Transmission Fourier Transform Infrared Spectroscopy, Raman Spectroscopy, Attenuated Total Reflectance Infrared Spectroscopy, or Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy. 
   
   
       5 . The process of  claim 5  wherein the method is Attenuated Total Reflectance Fourier Transform Infrared Spectroscopy.